Energy Management for a Fuel Cell Hybrid Vehicle

Hello Readers,
My name is Sharana basava, and I work as a junior software engineer at Luxoft India. I'm happy to share this post, in which I relate my previous experience with Energy Management for a Fuel Cell
Hybrid Vehicle.

INTRODUCTION

Nowadays, Fuel Cell Hybrid Vehicles (FCHV) represent a solution of increasing interest for car manufacturers. Some examples are Hyundai (TUCSON), General Motors (Chevrolet Equinox), Honda (FCX-V4 and FCX Clarity), Toyota (Toyota Mirai) and Volkswagen (Passat Lingyu). Nevertheless, some issues associated with hydrogen (H2) production, distribution and storage, and fuel cell cost and lifetime, have to be improved to make this technology more profitable and affordable. A complete description of characteristics and challenges of FCHV is presented in Fuel Cells (FC) offer two main advantages compared with internal combustion engines: higher efficiency and zero emissions from
the onboard source of power. However, FCs present some limitations associated with their slow transient response,which must be taken into account to avoid premature degradation. The reported literature points out that fast power variations cause conditions that promote the damage of the FC.To cope with highly changing power profiles, FCHVs incorporate an energy storage system. Additionally, this energy storage system allows to recover energy from braking. In most cases, a battery is adopted for such purpose, but also, if the battery size is large enough, it is possible to propel the vehicle during a long period without using the FC.In these cases, the vehicle can be recharged from the electrical grid, and the FC allows to extend the vehicle autonomy. These vehicles are known as plug-in or range extender hybrid vehicles.
Usually, they operate using only the battery until a certain level of charge, and then turn on the FC to supply electric energy to the vehicle and/or recharge the battery. The energy management strategy (EMS) in FCHV affects both global efficiency and lifetime of the components.A review of EMS for FCHV presented in points out that the Equivalent Consumption Minimization Strategy (ECMS), In recent years, due to emission reduction policies, research focused on alternative powertrains among which electric vehicles powered by fuel cells are becoming an attractive solution. Especially, proton-exchange fuel cell has more and more applications in hybrid vehicle.
The main issues of these vehicles are the energy management system and the utilization rate of the fuel. In order to optimize the performance of fuel cells and reduce fuel consumption, the best control solution is to power a vehicle with both fuel cell and battery. To model the hybrid powertrains behavior, a simulation program has been made and implemented in MATLAB/Simulink. In particular, the fuel cell type is selected as proton-exchange fuel cell and the battery is lead-acid battery. The fuel cell provides the normal required power for electric vehicles running, whereas the battery model also accounts for the charge/discharge efficiency. The hybrid powertrains are equipped with an energy management system. During acceleration, power is provided by the storage battery discharging, while during deceleration the battery is recharged. The control strategies assume charge maintaining operation of the battery, and the fuel cell system must work around its maximum efficiency. The feasibility for energy management is proved by simulation experiment.

*THE ENERGY CHAIN *

The overall structure studied in this work. It is based on associating a DC/DC converter led with a control loop for each source. The converter associated to the main source (FC) is an unidirectional boost converter. To interfacing the SC and the Bat to the DC link, two bidirectional converters are used to ensure the energy transfer in both directions: From the storage device to the load in traction mode and from load to storage device in breaking mode.

VEHICLE MODEL

The study presented in this work is based on tests performed
with the vehicle shown in Fig. 1-a. This vehicle is used daily in an eco-friendly vineyard, which produces electricity and hydrogen from solar energy. The vehicle was originally pure electric [15], designed for bumpy and irregular terrain, typically for agricultural and industrial tasks. In order to extend its autonomy, a Proton Exchange Membrane FC was added . The original vehicle has 41 MJ of electric energy available from the batteries, and this amount was increased to around 73 MJ with the addition of a FC
system, which notably extended its autonomy (up to 78 %).sumarizes some characteristics of the modified vehicle.Detailed information about this and the remodeling process can be found.
According to the configuration the power at the wheels is provided by the Electric Machine (EM) through the Differential. The EM can also work as generator to recover energy from braking. The vehicle has three gears with manual shift, and the regenerative braking only works in the lowest gear. The EM is connected to the direct current bus (DC-BUS) through an electronic converter. Then, the FC delivers power through the boost converter to the DC-BUS. Note that the voltage of the DC-BUS is determined by the battery voltage. The model of the powertrain used to evaluate the energy consumption and the power demands is focused on the efficiency of components, neglecting most of the component dynamics. Accordingly, the electronic converters and the EM are included in the model through their efficiencies. In the following sections, the battery and the FC model are described and the FCHV model used for the simulation is presented.

Battery
The battery used in the model is a lead-acid battery and provides 288V×13.9Ah. The reason for selecting this kind battery is that it represents a good compromise between cost and technical performance.
The battery state of change (SOC) is calculated using the “current integration method” implemented in a similar fashion in advisor. The efficiency of the battery is calculated on the bases of its SOC, and its
current is calculated using this equation:

where
Pb is the output power of the battery,
Rint and Rt is the internal resistance and the terminal Ohmic resistance, respectively,
Voc is the open circuit voltage.